The photocopying and laser printing industry is tending towards a dry type, monocomponent developer which does not contain carrier particles. In a developing apparatus using the monocomponent developer, the toner particles are triboelectrically charged by friction with a developer carrying member to a polarity suitable for developing the latent image. In that area of the developer carrying member which is opposed to a non image area (background) of the image beating member, the developer is not consumed. If the state of this no consumption of the developer continues, a layer of fine developer particles is strongly deposited thereon, presumably due to the electrostatic image force, and the particles are not easily consumed for development of the image area of the image beating member once the strong deposition is established. In addition, the existence of such a strongly deposited layer decreases the amount of charge of the developer present on the strongly deposited fine particle layer. This results in production of a ghost image on the developer image thus deteriorating the image quality.
Further, it is believed that particle size distribution in the bottom most toner layer on the developing sleeve is different in the toner consumed portion than the not consumed portion. More particularly, the fine particle layer is formed at the bottom of the non consumed portion. Since a fine particle has a larger surface area per unit volume, the amount of triboelectric charge per unit weight is greater than a larger size particle. Therefore, the fine particles are more strongly attracted to the developer carrying member by the electrostatic force due to the image force. Thus, the toner particles outside the portion where the fine particle layer is formed are not sufficiently triboelectrically charged by friction with the developing sleeve, and therefore, their developing power decreases, and they appear as a ghost on the image.
Also, when the developing sleeve is made of aluminum based materials, oxidation may form. The oxidation acts as an insulator and adversely effects the necessary charge for developing the latent image.
A number of techniques have been developed to enhance the image quality. Specifically, there are a number of patents which have roughened the surface of roller by blasting the surface with regular and/or irregular particles. A developing apparatus provided with a sleeve having a roughened surface is disclosed in U.S. Pat. Nos. 4,377,332, 4,300,966, and 4,807,461 corresponding to a Japanese laid-open Patent Application No. 131586/1989. In Japanese laid-open Patent Applications No. 116372/1982 and 11974/1983, a sleeve having a developer carrying surface blasted with a regular particles and/or regular particles is disclosed.
While stainless steel sleeves offer improved resistance to oxidation, the material cost as well as the processing costs reduces the economic appeal of such sleeves. In addition, aluminum based sleeves, while cheaper in material costs require coatings to provide sufficient oxidation resistance. Therefore, the need exists for magnetic roller sleeve formed of a cost effective material. The need also exists for the roller to have sufficient oxidation resistance without requiring additional coatings or processing.